Quantitative research on thermodynamic process and efficiency of a LNG heavy-duty engine with high compression ratio and hydrogen enrichment

Abstract

The effects of high compression ratio combining hydrogen enrichment on thermodynamic process and the consequent efficiency are experimentally evaluated on a LNG heavy-duty engine. The results indicate that increasing compression ratio and hydrogen enrichment have similar effects on the improvement of thermodynamic process. With increased compression ratio and hydrogen content, the peaks of cylinder pressure and pressure rise rate increase, ignition advances and combustion duration shortens. Moreover, combustion stability improves. Effective expansion ratio (EER) is in good agreement with indicated efficiency. The increase in compression ratio and hydrogen content can attain higher EER by improving thermodynamic process, and consequently achieve higher indicated efficiency. As hydrogen contents increase to a certain value, however, the thermal efficiencies may decrease, and NOx emissions continue to increase. Therefore, hydrogen content should be controlled in a proper proportion to achieve a balance between efficiency and emission. In the current study, the maximum loads cannot be affected as the compression ratio increases from 10.6 to 13.6, and the ultimate improvement of brake efficiency can reach 6% by the combination of high compression ratio and hydrogen enrichment. This effectively demonstrates their potential for improving thermodynamic process and efficiency of natural gas engines.